effective graphing for cartographers sp 240 cartography alex chaucer

Effective Graphing for Cartographers

SP 240 CartographyAlex Chaucer

Spatial Information Technology

Center

What is a graph?

• Must have a mathematical basis for construction• Chart and diagram can be used for those such as drawings, pictograms,

and organization-based drawings for which there may be no mathematical basis

Philosophical Foundations1. Graphicacy – skill necessary for communication of relationships

that cannot be expressed with words or mathematics (other forms – literacy, numeracy, articulacy)

2. Graphic Communication is a part of human communication. Human communication is composed of

1. Communicator (the one “sending”)2. Interpreter (the reader)3. Communication content (the message)4. Communication situation (perceived need to communicate)


Center

Brief History of Graphing• Pre-Christian Times

early gridding attempts at Lat/Long geometry

• Middle Ages planetary graphs

• Age of Enlightenment censuses, analytic geometry, early statistical graphs

• Age of Enthusiasm several European statistical conferences

• Early 19th Century early textbooks on graphics, attempts at standards

• Modern Day graphing aided by microcomputers


Center

Perception and the Graph

• Tasks from simple more complex• Most Accurate to least accurate (more

perceptual problems)1. Position along a common scale2. Position along identical, nonaligned scales3. Length4. Angle-slope5. Area6. Volume7. Color hue-color saturation-density


Center

Elements of the Standard Graph

• Data region• Scale lines• Vertical

Scale• Horizontal

Scale• Scale labels

• Data path• Reference

line• Markers• Key, legend• Data labels• Titles• Data sources


Center

Graph Planning in the Visual Hierarchy

• Similar concepts to design involved in creating a map

• Contrast can be used to get the reader’s attention

• Grid may be beneficial to include


Center

The Graphing Display of Numbers and Frequency

• Number display is oftern needed• There are numerous ways to display the

numbers• Often just including a table is not enough


Center

Histograms

• Graphic records of the occurrence of data values in a statistical distribution

• They represent a statistical distibution better then if just displayed in a table

• Permit an easy inspectin of how the data values are arrayed along a number line

• Allow the reader to gather a rather detailed picture of overall data characteristics


Center

Frequency Polygons and Frequency Distributions

• Frequency polygon – created by joining the tops of the bars in a histogram

• May create the frequency curve• If the data is reordered into an ascending

format, then it is known as a Lorenze Curve


Center

Ogives and Probability Graphs

• Ogive – a cumulative percentage graph• Given the name by Sir Francis Galton

(1822-1911) due to the resemblance to the curved rib of a Gothic vault

• By changing the horz. And vert. Axis an ogive can become a probability graph


Center

Box-Whisker Plots

• A box is drawn to that certain horizontal lines within and at the edges of box, aligned to the vertical axis of the graph, represent percentile values of the distribution

• Commonly percentile of 10, 25, 50, 75, 90 are represented


Center

Showing How Much of Something

• Linear Dot Graph• Common Bar Graph

One of the oldest forms of graphing Shows comparative amounts Clock graph (used by meteorologists for wind)

• Sector Graph Often called the pie graph Angles represent percentages; should not be done in 3D

• Trilinear Graph Soil – texture graph is common


Center

Showing Trends and Two-Variable Relation Graphs

• There are numerous ways to show trends and relationships within data

Line Graphs Scatterplots Logarithmic Graphs


Center

Simple and Compound Line Graphs

• Line Graph To show the relationship between two variables

Simple Line Graphs (time on the horizontal axis) Compound Line Graphs (multiple variables)


Center

The Scatterplot

• To see the mathematical relationship visually

Vertical axis is dependent Horizontal axis is independent Each data point represents a paired value

• Often used to find statistical correlation May lead to finding a regression line Looks for a relationship between variables


Center

The Logarithmic Graph

• Must have a logarithmic scale on one axis

• Purpose of these is to show a rate of change of one variable vs. another

effective graphing for cartographers sp 240 cartography alex chaucer

Documents